1. Field
The field relates to a system and a method for remote activation of downhole tools and devices used in association with wells for the production of hydrocarbons.
2. Description of Related Technology
Oil- and gas producing wells are designed in a range of different ways, depending on factors such as production characteristics, safety, installation issues and requirements to downhole monitoring and control. Common well components include production tubing, packers, valves, monitoring devices and control devices.
An extremely important consideration for all design and operations is to maintain a minimum number of barriers (e.g. 2) between the high-pressurised reservoir fluids and the open environment at the surface of the earth. Packers and valves are examples of commonly used mechanical barriers. Other barriers can be drilling mud and completion fluid which create a hydrostatic pressure large enough to overcome the reservoir pressure, hence preventing reservoir fluids from being produced.
Following the drilling stage; the installation of the production tubular, including a selection of the above described components and the wellhead is referred to as completing the well. During completion, temporary barriers are used to ensure that barrier requirements are adhered to during this intermediate stage. Such temporary barriers could be, for example, intervention plugs and/or disappearing plugs mounted in the lower end of the production tubing or the higher end of the well's liner.
Intervention plugs are typically installed and retrieved with well service operations such as wireline and coil tubing. Disappearing plugs are temporary barrier devices that are operated with pressure cycling from surface, i.e. surface pressure cycles are applied on the fluid column of the well to operate pistons located in the downhole device (disappearing plug). After a certain amount of cycles, the disappearing plug opens (i.e. “disappears”), hence the barrier is removed according to the well completion program.
Evolution of oil wells has included well designs such as multi lateral wells and side-tracks. A multilateral well is a well with several “branches” in the form of drilled bores that branch from the main bore. Multilateral wells allow a large reservoir area to be drained with one primary bore from the surface. A side track well is typically associated with an older production well that is used as the foundation for the drilling of one or more new bores. Hence, only the bottom section of the new producing interval needs to be drilled and time and costs are saved.
To sidetrack a well, the following operational method may be used:
One starts by installing a deep-set barrier in the wellbore, above the top of the old producing interval and below the kick-off point for the new branch to be drilled.
A whipstock is installed—this is a wedge shaped tool utilised to force the drill bit into the wall of the wellbore and into the formation.
The branch is drilled.
The branch is completed with the preferred selection of completion components.
The temporary barrier in the original bore is removed, if possible.
The well is put on production, producing from both the new and the old bore.
The new well designs (i.e. branches) have introduced a new challenge in the form of inaccessible areas of the well. Traditional operation of the above described temporary barrier systems may no longer be possible. Well intervention strings are normally not operated below junctions of branch wells, as the risk of getting stuck or causing other types of damage is considered too high. Also, in a branch well, one does not normally manage to seal off all rock faces, hence pressure cycling to operate traditional disappearing plugs might not be possible as the exposed rock may prevent the generation of pressure cycles of the required amplitude. Accordingly, the internal piston (or bellows or other similar mechanism) arrangements of the disappearing plugs cannot be operated.
In addition, certain specific completion methodologies for the new branch of a sidetrack well, for example if the branch's liner top is attached to the original well bore, or the whipstock being left in the well after sidetracking, will make the old producing interval totally non-accessible. Again, this will represent challenges with respect to the removal of traditional, temporary deep-set barriers.